Scroll compressor machines, which have two intermeshed involutes or scrolls, provide an efficient way to compress fluids, including gases or mixtures thereof. In operation, one of the scrolls is fixed and the other, an orbiting scroll, is driven by a motor so that it orbits in relation to the fixed scroll. Fluid enters the compressor shell through a low-pressure fluid inlet port and exits through a high-pressure discharge port. The low pressure fluid enters the outer pockets defined by the intermeshed scrolls and is moved toward the center of the intermeshed scrolls or spirals, thereby decreasing in volume and increasing in pressure. The compressed fluid is exhausted through the high-pressure discharge port to the refrigeration or cooling system.
Discharge check valves may be installed in the high-pressure discharge port of the compressor shell to prevent the return of high-pressure refrigerant fluid that may cause reverse movement of the orbiting scroll upon shut down of the compressor.
U.S. Pat. No. 5,141,420 and U.S. Pat. No. 6,171,084 both disclose disc type check valves in the discharge port area of a scroll type hermetic compressor. These valves contain a plurality of components, such as a valve housing, a valve seat element, a valve stop, and a valve disc, each of which must be precisely machined to ensure free movement of the valve disc. Typically, these disc type check valves include an unbiased, planar valve disc.
Such disc type discharge valves are mounted prior to, or in connection with, the welding or permanent attachment of a discharge fitting to the compressor shell. The discharge fitting allows the attachment of suitable conduits to the compressor shell from the rest of the refrigeration system. With these known discharge check valves, once the discharge fitting is attached to the compressor shell, the discharge check valves cannot then be added. Moreover, once these known discharge check valves are assembled to the compressor shell, they cannot be removed without also detaching the discharge fitting from the compressor shell.
Further, these disk type valves are not completely tight, due to insufficient closure force on the unbiased valve element and manufacturing tolerances for the valve element and the valve seat. Even if reverse rotation of the compressor can be avoided when the compressor stops, a certain amount of refrigerant will leak back from the high-pressure side of the refrigeration system into the compressor shell.
In multi-compressor systems, this leads to preservation of high pressure in the discharge compartment inside the hermetic shell of the compressor, when the compressor stops. Due to this elevated pressure, restarting the compressor requires a higher than normal starting torque.